The present invention relates to a packing container of the type which has a sealing fin.
A known and frequently encountered packing container for the packing e.g. of milk is manufactured from a flexible, weblike laminate which comprises a central carrier layer of paper coated on both sides with thin layers of liquid-tight, heat-sealable plastic material, e.g. polyethylene. The laminate is supplied to a packing machine in the form of a roll and is converted on being rolled off the roll successively to tubular form and at the same time has its longitudinal edges are sealed to one another in liquid-tight manner. The tube is fed substantially vertically downwards through the packing machine. The tube is supplied continuously with contents via a pipe which extends into the tube at the upper end of the same. By means of level-controlling elements it is ensured that the surface of the contents is constantly maintained at a certain level. Below this level subsequently a repeated transverse sealing of the tube takes place. The tube is compressed at equal intervals with the help of heated sealing jaws, as a result of which the heat-sealable plastic layers present on the inside of the tube join the tube sides together in liquid-tight, transverse sealing zones. Thus a series of coherent, substantially cushion-shaped packing containers is produced, which are separated from one another by cutting through the sealing zones. Further shaping of the filled cushion-shaped containers gives these a final, substantially parallelepipedic form. In this final shaping process four double-walled corner lugs appear which are formed of material which for geometrical reasons can not be utilized in the formation of the actual parallelepipedic container body. So as not to be in the way or interfere with the regular parallelepipedic shape these flattened corner lugs are folded against and are sealed to adjoining packing container surfaces. The packing container is now finished.
As is evident from the above, cushion-shaped packing containers result from the transverse sealing and cutting off of the filled material tube. The packing containers at their upper and lower end are provided with sealing fins. After conversion of the cushion-shaped container to parallelepipedic shape, these sealing fins will extend substantially centrally over the upper and lower end wall of the packing container as well as over the corner lugs adjoining these end walls. The sealing fin thus extends transversely over the end wall of the packing container between the two free corners of the corner lugs adjoining the end wall. In connection with the shaping of the parallelepipedic packing container the sealing fins are folded down so that they rest against the material surface to which they are connected. As mentioned earlier, the flattened corner lugs are folded in and attached to adjoining container walls. The two corner lugs present at the bottom end of the packing container are usually folded against the bottom of the packing container. This folding is rendered difficult, however, by the sealing fin running over the bottom end as well as over the two corner lugs. When a corner lug is folded in to rest against the bottom of the packing container it is thus necessary to fold over 180.degree. not only the two material layers which form the corner lug itself but also the sealing fin formed of two material layers. Consequently, after folding in and attachment to the bottom of the packing container the corner lug will not be wholly plane but will somewhat bulge outwards. This is of course a disadvantage, since the packing container will consequently stand up less well when put in upright position on a plane surface.
The folding over 180.degree. of the corner lug and the sealing fin extending over the corner lug is difficult to perform, owing to the manifold material thickness, in such a manner that the folding line becomes well defined and sharp. Earlier attempts to improve and simplify the folding with the help of folding lines and crease lines have been largely unsuccessful, since in spite of these expedients the folding gives rise to a compressed accumulation of material in the line of intersection between the sealing fin and the folding line. Consequently the material layers which after folding are located on the "outside" of the folding (that is to say the material situated outside the eventual neutral plane) will be subjected to very strong tensile stresses with attendant stretching and crack formations. These tensile stresses are so great that the layers of thermoplastics included in the laminate frequently crack and leakages occur as a consequence. When the laminate also contains layers of aluminium foil, which is frequently the case, crack formation is almost unadvoidable, since the aluminium foil has appreciably inferior stretching properties compared to the properties of the thermoplastic material.
To avoid the abovementioned disadvantages it has been endeavoured up to now, among other things, to increase to the greatest possible extent the elasticity of the materials included. This solution gives relatively good results insofar as the thermoplastic layers are concerned, but does not solve the problem of any aluminium layers included in the laminate.
It is an object of the present invention to provide a packing container which, while being of substantially the same design as earlier packing containers, avoids the aforementioned problems and makes it possible to fold the corner lugs in against the bottom surface of the packing container without the sealing fin which extends over the lug causing problems of the aforementioned kind.
It is a further object of the present invention to provide a packing container which is simple to manufacture and which only requires a slight modification of present manufacturing machines.
It is a further object of the present invention to provide a packing container where the folding in of the corner lugs against the wall surfaces of the packing container is facilitated and where the corner lugs after folding in retain a generally plane shape.
Finally it is an object of the present invention to provide a packing container where the folding in of the corner lugs and the sealing fin extending over the corner lugs can be carried out without any risk whatever of crack formation occuring in the material layers of the packing laminate.
These and other objects have been achieved in accordance with the present invention in that a packing container of the type described in the introduction has been given the characteristic that a portion of the sealing fin extending over the packing container wall is folded down against the wall in one direction, while a portion of the sealing fin extending over the corner lug is folded down against the corner lug in the opposite direction.
Preferred embodiments of the packing container in accordance with the invention have moreover been given the characteristics evident from the subsidiary claims.